Every year 250-300 million dollars of chemical pesticides are used to control corn rootworm infestations. Many of these chemical pesticides are toxic to humans, wildlife and other nontarget species. In addition, some of these pesticides have been found in ground water. New chemical pesticides cost $100 million to develop.
Biological control offers an attractive alternative to synthetic chemical pesticides. Biopesticides (living organisms and the naturally-occurring compounds produced by these organisms) can be safer, more biodegradable, and less expensive to develop.
One commonly used biopesticide is the gram-positive bacterium Bacillus thuringiensis. Pesticidal B. thuringiensis strains are known to produce crystal proteins during sporulation that are specifically toxic to certain orders and species of insects and nematodes (See, e.g., U.S. Pat. Nos. 4,999,192 and 5,208,017). Proteinaceous endotoxins produced by B. thuringiensis also act as insecticidal agents against corn rootworm and other beetles (e.g., U.S. Pat. No. 5,187,091, and Johnson et al. (1993) J. Economic Entomology, 86: 330-333). B. thuringiensis endotoxins have been shown to be effective pesticides in the form of purified crystals, washed cell pellets, and expressed proteins. Warren et al. (WO 96/10083) discloses non-endotoxin proteins produced during the vegetative stage of Bacillus cereus and B. thuringiensis. These vegetative proteins, designated Vip1 and Vip2, have potent insecticidal activity against corn rootworm (northern and western) (Estruch et al. (1997) Nature Biotechnology 15:137-141 and Mullins et al. (1997) Appl Environ. Microbiol. 63 (in press).
One B. thuringiensis thermostable-metabolite designated beta-exotoxin has also been shown to have pesticidal properties. Burgjeron and Biache (1979) Entomophaga II:279-284 report a beta exotoxin that is active against Colorado potato beetle (Leptinotarsa decemlineata). In addition, the known B. thuringiensis beta-exotoxins exhibit non-specific pesticidal activity, killing not only nematodes, but also flies, armyworms, mites, and corn rootworms. Sigma-exotoxin has a structure similar to beta-exotoxin, and exhibits pesticidal activity against Colorado potato beetle (Argauer et al. (1991) J. Entomol. Sci. 26:205-213). Alpha-exotoxin is toxic to larvae of Musca domestics (Luthy (1980) FEMS Microbiol. Lett. 8:1-7). Gamma-exotoxins are various proteolytic enzymes, chitinases and proteases. The toxic effects of gamma-exotoxins are only expressed in combination with beta-exotoxin or delta-endotoxin. Forsberg et al. (1976) "Bacillus thuringiensis: Its effects in Environmental Quality," National Research Council of Canada. Stonard et al. (1994) ACS Symposium Series 551: 25 report a water-soluble secondary metabolite exhibiting pesticidal activity against corn rootworm in the supernatant of a Bacillus cereus strain.
There are no documented strains of Rhodococcus sp. that produce metabolites exhibiting pesticidal activity against corn rootworms. Moreover, there are no known solvent-extractable metabolites produced by Rhodococcus sp. with pesticidal activity against corn rootworms.